Control unit and control method for torque-demand-type internal combustion engine

ABSTRACT

When a fuel-supply cutoff condition is satisfied, an ECU executes a program including: calculating the target torque; detecting the engine speed NE; calculating the target KL based on the target torque, NE and MBT; controlling an engine using the throttle valve opening amount based on the target KL, the base fuel ignition timing, and the fuel injection amount based on the current KL until the target KL becomes equal to or lower than the KL lower limit; controlling the engine using the throttle valve opening amount based on the KL lower limit, NE, the target ignition timing calculated based on the current KL and the target torque, and the fuel injection amount based on the current KL when the target KL reaches the KL lower limit; and actually starting a fuel-supply cutoff when the target ignition timing reaches the retardation limit timing.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to a control unit and control method foran internal combustion engine, which executes a fuel-supply cutoffcontrol, and, more specifically to a fuel-supply cutoff control executedover an internal combustion engine of which the operating state isadjusted to control the output torque (hereinafter, this type ofinternal combustion engine will be referred to as “torque-demand-typeinternal combustion engine”).

2. Description of the Related Art

In many types of vehicles provided with an internal combustion engine(hereinafter, referred to as “engine” where appropriate), a so-calledfuel-supply cutoff control, that is, a control for cutting off the fuelsupply, is executed while the vehicle is decelerating in order toenhance the fuel efficiency. The fuel-supply cutoff control is executedin order to enhance the fuel efficiency by minimizing the amount of fuelthat is supplied to the engine without impairing the travelingperformance of the vehicle and riding comfort. Usually, when the enginespeed is within a predetermined engine speed range (when the enginespeed is equal to or higher than a fuel-supply cutoff speed) while thevehicle is decelerating with the engine idling, the fuel supply is cutoff. More specifically, the fuel supply is cut off when a throttle valveis closed while the vehicle is traveling and the engine speed is equalto or higher than the fuel-supply cutoff speed. Also, when the enginespeed decreases to a fuel-supply restart speed that is the lower limitof the engine speed range, the fuel supply is restarted in order toprevent engine stalling.

More specific description will be provided below. When the vehicle istraveling using an inertia force, that is, the vehicle is coasting, forexample, when the vehicle is decelerating, the engine is forciblyrotated by an external force and kept rotating. The fuel-supply cutoffcontrol is executed while the engine speed is in an engine speed rangein which the engine keeps rotating by itself. In other words, the fuelsupply is restarted when it becomes impossible for the engine to rotateby itself. Namely, while the vehicle is decelerating, the fuel supply iscut off until the engine speed decreases to the fuel-supply restartspeed.

If a control is executed so that it takes longer for the engine speed todecrease to the fuel-supply restart speed, the time period in which thefuel supply is cut off is prolonged, which further enhances the fuelefficiency. Therefore, in conventional technologies, components thatconstitute a drive power system (power train system) from an engine todrive wheels are substantially directly connected to mechanically eachother in order to minimize a decrease in the engine speed due to,so-called, slippage in the drive power system. In an example of suchcontrol, the engine speed during deceleration is made relatively high byengaging a lock-up clutch (direct-connection clutch) of a hydraulicpower transmission device, for example, a torque converter.

Because the lock-up clutch connects an input-side member to anoutput-side member mechanically instead of using fluid, the lock-upclutch also transfers torque fluctuations without moderating them. Thismay cause a shock and vibration when the fuel-supply cutoff control isstarted.

Japanese Patent Application Publication No. JP-2001-342878(JP-A-2001-342878) describes a control unit for an internal combustionengine, which makes it possible to minimize such shock and vibration.The control unit for an internal combustion engine executes afuel-supply cutoff control for cutting off the fuel supply to theinternal combustion engine while the vehicle is traveling. The controlunit includes at least one of an immediately-before fuel-supply cutofftorque control unit and an immediately-after fuel-supply cutoff torquecontrol unit. The immediately-before fuel-supply cutoff torque controlunit decreases the torque directed from the internal combustion enginetoward drive wheels in a drive power system, which is from the internalcombustion engine to the drive wheels, immediately before execution ofthe fuel-supply cutoff control if it is determined that the fuel-supplycutoff control should be executed. The immediately-after fuel-supplycutoff torque control unit increases the torque directed from theinternal combustion engine toward the drive wheels in the drive powersystem immediately after start of the fuel-supply cutoff control.

In the control unit for an internal combustion engine, if it isdetermined that the fuel-supply cutoff control for cutting off the fuelsupply to the internal combustion engine when the vehicle is travelingshould be executed, the torque directed from the internal combustionengine toward the drive wheels is decreased immediately before executionof the fuel-supply cutoff control. As a result, when the torque outputfrom the internal combustion engine is decreased due to execution of thefuel-supply cutoff control, the torque directed toward the drive wheelshas been decreased to a certain degree. Therefore, the amount of changein the torque received by the drive wheels, which is caused due toexecution of the fuel-supply cutoff control, is reduced. When thecontrol unit for an internal combustion engine includes theimmediately-after fuel-supply cutoff torque control unit, a control forincreasing the torque directed toward the drive wheels in the drivepower system is executed immediately after start of the fuel-supplycutoff control. Therefore, a decrease in the torque output from theinternal combustion engine and an increase in the torque caused by theimmediately-after fuel-supply cutoff torque control unit cancel eachother. As a result, even if the torque output from the internalcombustion engine decreases due to execution of the fuel-supply cutoffcontrol, the amount of change in the torque received by the drive wheelsand the drive power system is reduced.

In a vehicle provided with an engine of which the output torque iscontrolled independently of an operation of an accelerator pedalperformed by a driver, and an automatic transmission, a “drive powercontrol” may be executed. In the drive power control, a target drivetorque, which takes a positive value or a negative value and which iscalculated based on the amount by which the accelerator pedal isoperated by the driver (hereinafter, referred to as “accelerator pedaloperation amount” where appropriate), the operating conditions of thevehicle, etc. is achieved by controlling the engine torque and the gearratio of the automatic transmission. Controls such as a “drive powerrequiring control”, a “drive power demand control”, and a “torque-demandcontrol” are similar to the drive power control.

A torque-demand engine control unit calculates a target torque whichshould be output from an engine based on the accelerator pedal operationamount, the engine speed, and the external load, and controls the fuelinjection amount and the air supply amount based on the target torque.This torque-demand engine control unit actually calculates a targetgeneration torque by adding loss load torques, such as a frictiontorque, that are lost in the engine and a power train system to therequired output torque. The engine control unit then controls the fuelinjection amount and the air supply amount so that the target generationtorque is achieved. The torque-demand engine control unit improves thedriving performance, for example, makes it possible to always maintain aconstant driving feel, by adjusting the engine torque, which is aphysical quantity that directly exerts an influence on the vehiclecontrol, to a reference value. That is, the torque required by theentire vehicle including the engine and the power train system and thetarget torque are matched with each other by controlling the engine andan automatic transmission (including a lock-up clutch).

In addition, if the torque-demand control method is employed only forthe engine (that is, only the engine is a control target and theautomatic transmission is not a control target), only the engine iscontrolled to output a target torque required of the engine.

That is, the throttle valve opening amount, the ignition timing, and thefuel injection amount, at which the target torque is achieved, arecalculated based on the relationship among the engine speed NE, theintake efficiency KL (=amount (mass flow) of air taken intocylinder/maximum amount (mass flow) of air that can be taken incylinder), the ignition timing SA (hereinafter, ignition timing will bereferred to as “SA” (Spark Advance) where appropriate), the air-fuelratio A/F (stoichiometric air-fuel ratio may be used), and the torque.Namely, in the engine torque-demand control described above, an engineECU (Electronic Control Unit) calculates a target engine torque andcontrols the throttle valve opening amount, the ignition timing and thefuel injection amount to achieve the target torque.

However, according to JP-A-2001-342878, only a throttle valve and anidle speed control valve are used to decrease the torque immediatelybefore cutting off the fuel supply or increase the torque immediatelyafter the fuel supply is restarted in response to a command toaccelerate the vehicle issued by the driver. That is, the torque outputfrom the engine is controlled only by adjusting the intake air amount.As a result, it is sometimes difficult to achieve the required torque.

SUMMARY OF THE INVENTION

The invention provides a control unit and control method for atorque-demand-type internal combustion engine suitable for a fuel-supplycutoff control, which minimizes a shock that is likely to be caused whena fuel-supply cutoff is started and a fuel supply is restarted.

Examples of a control unit for a torque-demand-type internal combustionengine described below include a control unit that is used when a torquerequired of an engine is achieved by an engine control system in thecase where a target torque required by an entire vehicle including theengine and a power train system needs to be achieved.

A first aspect of the invention relates to a control unit for atorque-demand-type internal combustion engine mounted in a vehicle. Thecontrol unit includes: a determination unit that determines that afuel-supply cutoff for cutting off a fuel supply to the internalcombustion engine is allowed to start when the state of the vehiclesatisfies a predetermined fuel-supply cutoff start condition; and acontrol unit that executes a torque-demand control using therelationship established among at least an intake efficiency, a torqueand an engine speed. The control unit includes an intake efficiencycontrol unit, that decreases the intake efficiency of the internalcombustion engine to decrease the torque generated by the internalcombustion engine before executing the fuel-supply cutoff, when it isdetermined that the fuel-supply cutoff is allowed to start, and anignition timing control unit that retards ignition timing of theinternal combustion engine to decrease the torque generated by theinternal combustion engine, after the intake efficiency of the internalcombustion engine is decreased. The control unit further includes afuel-supply cutoff control unit that controls the internal combustionengine to execute the fuel-supply cutoff after the ignition timing ofthe internal combustion engine is retarded.

According to the first aspect of the invention, the fuel-supply cutoffis not started yet when the vehicle state satisfies the predeterminedfuel-supply cutoff start condition. Before execution of the fuel-supplycutoff, the intake efficiency of the internal combustion engine isdecreased to decrease the torque, and then, the ignition timing isretarded to decrease the torque. In this way, the fuel-supply cutoff isactually executed after the intake efficiency is decreased and theignition timing is retarded. The torque-demand control is employed inthe control for decreasing the intake efficiency and the control forretarding the ignition timing. Thus, the fuel-supply cutoff is executedafter the torque output from the internal combustion engine is smoothlydecreased by a sufficient amount. Therefore, it is possible to reduce astepwise change in the torque. Accordingly, it is possible to reduce ashock that is caused when the fuel-supply cutoff is started. As aresult, it is possible to provide the control unit for atorque-demand-type internal combustion engine suitable for thefuel-supply cutoff control, which minimizes a shock that is likely to becaused when the fuel-supply cutoff is started.

A second aspect of the invention relates to the control unit accordingto the first aspect of the invention, in which the intake efficiencycontrol unit decreases the intake efficiency to a predetermined lowerlimit value.

According to the second aspect of the invention, the ignition timing isretarded after the intake efficiency is decreased to the lower limitvalue that is the lower limit of the a range in which the fuel injectedfrom an injector is ignited. Therefore, it is possible to execute thefuel-supply cutoff after the torque output from the internal combustionengine is decreased by a sufficient amount.

A third aspect of the invention relates to the control unit according tothe first aspect of the invention, in which the ignition timing controlunit retards the ignition timing to predetermined retardation limittiming.

According to the third aspect of the invention, it is possible to reducea stepwise change in the torque, which is likely to be caused when thefuel-supply cutoff is executed, because the fuel-supply cutoff isexecuted after the ignition timing is retarded to the retardation limittiming.

A fourth aspect of the invention relates to the control unit accordingto the third aspect of the invention, in which the ignition timingcontrol unit calculates the ignition timing using the actual intakeefficiency.

According to the fourth aspect of the invention, when the torque-demandcontrol is executed using the relationship established among the intakeefficiency, the torque and the engine speed to retard the ignitiontiming, the ignition timing is calculated using the actual intakeefficiency. Therefore, it is possible to accurately retard the ignitiontiming to the retardation limit timing.

A fifth aspect of the invention relates to the control unit according tothe third or fourth aspect of the invention, in which the fuel-supplycutoff control unit controls the internal combustion engine so that thefuel-supply cutoff is executed when the ignition timing of the internalcombustion engine is retarded to the retardation limit timing.

According to the fifth aspect of the invention, when the ignition timingof the internal combustion engine is retarded to the retardation limittiming (when the torque required by the driver falls below the generablelimit torque), the torque generated by the internal combustion engine isdecreased to the fullest extent. Therefore, it is possible to minimize astepwise change in the torque caused when the fuel-supply cutoff isexecuted.

A sixth aspect of the invention relates to a control unit for atorque-demand-type internal combustion engine which is mounted in avehicle and which is suitable for a fuel-supply cutoff control, as thefirst aspect of the invention. The control unit includes: a fuel supplyrestart control unit that controls the internal combustion engine sothat a fuel supply is restarted when a predetermined condition issatisfied while a fuel-supply cutoff for cutting off a fuel supply tothe internal combustion engine is executed; and a control unit thatexecutes a torque-demand control using the relationship establishedamong at least an intake efficiency, a torque and an engine speed. Thecontrol unit includes an ignition timing control unit that advancesignition timing of the internal combustion engine to increase the torquegenerated by the internal combustion engine when the fuel supply isrestarted, and an intake efficiency control unit that increases theintake efficiency of the internal combustion engine to increase thetorque generated by the internal combustion engine after the ignitiontiming of the internal combustion engine is advanced.

According to the sixth aspect of the invention, when the vehicle statesatisfies the predetermined fuel supply restart condition while thefuel-supply cutoff is executed, the fuel supply is restarted (fuelinjection control and ignition control are restarted).

When the fuel supply is restarted, the ignition timing is advanced toincrease the torque, and then the intake efficiency is increased toincrease the torque. The torque-demand control is employed in thecontrol for advancing the ignition timing and the control for increasingthe intake efficiency. Thus, it is possible to smoothly increase thetorque output from the internal combustion engine by a sufficient amountafter the fuel supply is restarted. Therefore, a difference between theoutput torque and the torque required by the driver is reduced.Therefore, it is possible to reduce a shock caused when the fuel supplyis restarted. As a result, it is possible to provide the control unitfor a torque-demand-type internal combustion engine suitable for thefuel-supply cutoff control, which minimizes a shock caused when the fuelsupply is restarted.

A seventh aspect of the invention relates to the control unit accordingto the sixth aspect of the invention, in which the ignition timingcontrol unit advances the ignition timing to predetermined referenceignition timing.

According to the seventh aspect of the invention, after the fuel supplyis restarted, the ignition timing is advanced to the reference ignitiontiming (e.g. base ignition timing or ignition timing corresponding toMBT (Minimum spark advance for Best Torque)). Therefore, it is possibleto promptly increase the torque when the fuel supply is restarted.

An eighth aspect of the invention relates to the control unit accordingto the sixth aspect of the invention, in which the ignition timingcontrol unit calculates the ignition timing using the actual intakeefficiency, and advances the ignition timing to predetermined referenceignition timing.

According to the eighth aspect of the invention, when the torque-demandcontrol is executed using the relationship established among the intakeefficiency, the torque and the engine speed to advance the ignitiontiming, the ignition timing is calculated using the actual intakeefficiency. Therefore, it is possible to accurately advance the ignitiontiming to the reference ignition timing.

A ninth aspect of the invention relates to a method for controlling atorque-demand-type internal combustion engine mounted in a vehicle.According to the method, when the state of the vehicle satisfies apredetermined fuel-supply cutoff start condition, it is determined thata fuel-supply cutoff for cutting off a fuel supply to the internalcombustion engine is allowed to start. A torque-demand control isexecuted using the relationship established among at least an intakeefficiency, a torque and an engine speed. In the torque-demand control,when it is determined that the fuel-supply cutoff is allowed to start,before executing the fuel-supply cutoff, the intake efficiency of theinternal combustion engine is decreased to decrease the torque generatedby the internal combustion engine, and ignition timing of the internalcombustion engine is retarded to decrease the torque generated by theinternal combustion engine after the intake efficiency of the internalcombustion engine is decreased. After the ignition timing of theinternal combustion engine is retarded, the internal combustion engineis controlled to execute the fuel-supply cutoff.

A tenth aspect of the invention relates to a method for controlling atorque-demand-type internal combustion engine which is mounted in avehicle and which is suitable for a fuel-supply cutoff control.According to the method, when a predetermined condition is satisfiedwhile a fuel-supply cutoff for cutting off a fuel supply to the internalcombustion engine is executed, the internal combustion engine iscontrolled so that a fuel supply is restarted. A torque-demand controlis executed using the relationship established among at least an intakeefficiency, a torque and an engine speed. In the torque-demand control,when the fuel supply is restarted, ignition timing of the internalcombustion engine is advanced to increase the torque generated by theinternal combustion engine. After the ignition timing of the internalcombustion engine is advanced, the intake efficiency of the internalcombustion engine is increased to increase the torque generated by theinternal combustion engine.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and further features and advantages of the invention willbecome apparent from the following description of an example embodimentwith reference to the accompanying drawings, wherein the same orcorresponding portions will be denoted by the same reference numeralsand wherein:

FIG. 1 is a control block diagram for a vehicle provided with a controlunit according to an embodiment of the invention;

FIG. 2 is a control block diagram for the control unit according to theembodiment of the invention;

FIG. 3A and FIG. 3B are flowcharts showing a control routine executed byan engine ECU in FIG. 1 when the fuel-supply cutoff is started;

FIG. 4A and FIG. 4B is a flowchart showing a control routine executed bythe engine ECU in FIG. 1 when the fuel supply is restarted;

FIG. 5 is a timing chart that includes the time at which the fuel-supplycutoff is started and the time at which the fuel supply is restarted;

FIG. 6 is a detailed timing chart showing the state, shown in FIG. 5,when the fuel-supply cutoff is started;

FIG. 7 is a detailed timing chart showing the state, shown in FIG. 5,when the fuel supply is restarted;

FIG. 8 is a timing chart according to a first modified example of theembodiment of the invention; and

FIG. 9 is a graph showing the base torque according to a second modifiedexample of the embodiment of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENT

Hereafter, an embodiment of the invention will be described withreference to the accompanying drawings. In the description below, thesame components will be denoted by the same reference numerals. Becausethe names and the functions of the components having the same referencenumerals are also the same, the detailed description thereof will beprovided only once below. The following description will be provided onthe assumption that a torque-demand control is executed over an engine.

As shown in FIG. 1, a vehicle provided with a control unit according tothe embodiment of the invention includes an engine 150, an intake system152, an exhaust system 154, and an engine ECU 100. Although the engine150 is a port-injection gasoline engine, the engine 150 may be providedwith a direct-injection fuel injector that directly injects fuel into acylinder instead of or in addition to a port injector.

The intake system 152 includes an intake passage 110, an air cleaner118, an airflow meter 104, a throttle motor 114, a throttle valve 112,and a throttle position sensor 116.

The air taken in from the air cleaner 118 flows into the engine 150through the intake passage 110. The throttle valve 112 is provided in amiddle portion of the intake passage 110. The throttle valve 112 isopened and closed in accordance with the operation of the throttle motor114. The opening amount of the throttle valve 112 is detected by thethrottle position sensor 116. The airflow meter 104, which detects theintake air amount, is provided in the intake passage at a positionbetween the air cleaner 118 and the throttle valve 112. The airflowmeter 104 transmits an intake-air amount signal that indicates theintake air amount Q to the engine ECU 100.

The engine 150 includes a coolant passage 122, a cylinder block 124, aninjector 126, pistons 128, a crankshaft 130, a coolant temperaturesensor 106, and a crank position sensor 132.

A predetermined number of cylinders are formed within the cylinder block124, and the pistons 128 are provided in the respective cylinders. Themixture of the fuel injected from the injector 126 and the intake air isintroduced into a combustion chamber formed above the piston 128 throughthe intake passage 110, and ignited by a spark plug (not shown). Whencombustion takes place, the piston 128 is pushed down. The reciprocationof the piston 128 is converted into the rotation of the crankshaft 130via a crank mechanism. The engine ECU 100 detects the rotational speedNE of the engine 150 based on a signal from the crank position sensor132.

A coolant is circulated through the coolant passage 122 formed withinthe cylinder block 124 in accordance with the operation of a water pump(not shown). The coolant in the coolant passage 122 flows to a radiator(not shown) connected to the coolant passage 122 and cooled by a coolingfan (not shown). The coolant temperature sensor 106, which detects thetemperature THW of the coolant in the coolant passage 122 (enginecoolant temperature THW), is provided on the coolant passage 122. Thecoolant temperature sensor 106 transmits a signal that indicates thedetected engine coolant temperature THW to the engine ECU 100.

The exhaust system 154 includes an exhaust passage 108, a first air-fuelratio sensor 102A, a second air-fuel ratio sensor 102B, a firstthree-way catalytic converter 120A, and a second three-way catalyticconverter 120B. The first air-fuel ratio sensor 102A is provided at aposition upstream of the first three-way catalytic converter 120A, andthe second air-fuel ratio sensor 102B is provided at a positiondownstream of the first three-way catalytic converter 120A (upstream ofthe second three-way catalytic converter 120B). Instead of providing twothree-way catalytic converters, only one three-way catalytic convertermay be provided.

The exhaust passage 108 that is connected to an exhaust port of theengine 150 is connected to the first three-way catalytic converter 120Aand the second three-way catalytic converter 120B. That is, the exhaustgas generated due to the combustion of the air-fuel mixture, which takesplace in the combustion chamber of the engine 150, first flows into thefirst three-way catalytic converter 120A. HC and CO contained in theexhaust gas introduced into the first three-way catalytic converter 120Aare oxidized in the first three-way catalytic converter 120A. NOxcontained in the exhaust gas introduced into the first three-waycatalytic converter 120A is reduced in the first three-way catalyticconverter 120A. The first three-way catalytic converter 120A is providednear the engine 150. Even when the engine 150 is started while it iscold, the temperature of the first three-way catalytic converter 120A ispromptly increased and therefore the three-way catalytic converter 120Aexhibits its catalytic function promptly.

Then, the exhaust gas is delivered from the first three-way catalyticconverter 120A to the second three-way catalytic converter 120B in orderto remove the NOx. The first three-way catalytic converter 120A and thesecond three-way catalytic converter 120B basically have the samestructure and function.

The first air-fuel ratio sensor 102A, which is provided at a positionupstream of the first three-way catalytic converter 120A, and the secondair-fuel ratio sensor 102B, which is provided at a position downstreamof the first three-way catalytic converter 120A and upstream of thesecond three-way catalytic converter 120B, detect the oxygenconcentration in the exhaust gas that will pass through the firstthree-way catalytic converter 120A and the exhaust gas that will pasthrough the second three-way catalytic converter 120B, respectively. Itis possible to detect the ratio between the fuel and the air that arecontained in the exhaust gas, that is, the air-fuel ratio, by detectingthe oxygen concentration in the exhaust gas.

Each of the first air-fuel ratio sensor 102A and the second air-fuelratio sensor 102B generates an electric current having a magnitude thatcorresponds to the oxygen concentration in the exhaust gas. The currentvalue is converted into, for example, the pressure value, and a signalthat indicates the pressure value is transmitted to the engine ECU 100.Therefore, it is possible to detect the air-fuel ratio of the exhaustgas upstream of the first three-way catalytic converter 120A based onthe signal output from the first air-fuel ratio sensor 102A. Also, it ispossible to detect the air-fuel ratio of the exhaust gas upstream of thesecond three-way catalytic converter 120B based on the signal outputfrom the second air-fuel ratio sensor 102B. Each of the first air-fuelratio sensor 102A and the second air-fuel ratio sensor 102B generates avoltage of, for example, approximately 0.1 V when the air-fuel ratio ishigher than the stoichiometric air-fuel ratio, and generates a voltageof, for example, approximately 0.9 V when the air-fuel ratio is lowerthan the stoichiometric air-fuel ratio. The values obtained byconverting these voltage values into the air-fuel ratios and thethreshold value of the air-fuel ratio are compared with each other, andthe engine ECU 100 controls the air-fuel ratio based on the result ofcomparison.

The first three-way catalytic converter 120A and the second three-waycatalytic converter 120B each have a function of reducing NOx whileoxidizing HC and CO when the air-fuel ratio is substantially equal tothe stoichiometric air-fuel ratio, that is, a function of removing HC,CO and NOx at the same time. In the first three-way, catalytic converter120A and the second catalytic converter 120B, the oxidizing actionbecomes active but the reducing action becomes inactive when theair-fuel ratio is higher than the stoichiometric air-fuel ratio and theexhaust gas contains a large amount of oxygen, whereas the reducingaction becomes active but the oxidizing action becomes inactive when theair-fuel ratio is lower than the stoichiometric air-fuel ratio and theexhaust gas contains a small amount of oxygen. Therefore, it is notpossible to appropriately remove HC, CO and NOx at the same time.

An accelerator pedal operation amount sensor is connected to the engineECU 100, and detects the operation amount of an accelerator pedal, whichis operated by a driver.

The engine ECU 100 executes a torque-demand control over the engine 150.The engine ECU 100 calculates the throttle valve opening amount, theignition timing and the fuel injection amount, at which the targettorque is achieved, based on the relationship among the engine speed NE,the intake efficiency KL, the ignition timing SA, the air-fuel ratio A/F(stoichiometric air-fuel ratio is used in this case), and the torque.Then, the engine ECU 100 controls the opening amount of the throttlevalve 112, the ignition timing, and the amount of fuel injected from theinjector 126 (more specifically, the engine ECU 100 controls the fuelinjection duration to control the fuel injection amount in a region(fuel injection amount limit region) in which a linear relationship isestablished between the fuel injection duration and the fuel injectionamount).

In the engine torque demand control, the engine ECU 100 calculates thetarget torque that should be generated by the engine, and controls thethrottle valve opening amount, the ignition timing and the fuelinjection amount to achieve the target torque. In addition, the engineECU 100 calculates the throttle valve opening amount based on the targetintake efficiency KL, which is calculated based on the target torque,and controls the throttle valve 112 to achieve the calculated throttlevalve opening amount. Under this control, the opening amount of thethrottle valve 112 is adjusted and the intake efficiency KL changes. Thecurrent intake efficiency KL is detected, and the ignition timing iscontrolled based on the current intake efficiency KL.

FIG. 2 is a functional block diagram of the control unit according tothe embodiment of the invention. As shown in FIG. 2, the control unit(implemented by the engine ECU 100) smoothly decreases the torque outputfrom the engine 150 when cutting off the fuel supply, and promptlyincreases the torque output from the engine 150 immediately afterrestarting the fuel supply in response to an operation of theaccelerator pedal (acceleration command) performed by the driver. Atthis time, the torque-demand control is executed. The case in which thetorque output from the engine 150 is smoothly decreased immediatelybefore the fuel supply is cut off will be described below.

The following process is executed to decrease the torque output from theengine 150. A computing unit 1000 calculates a torque (target torque) byMultiplying the target torque used in the ISC (Idle Speed Control)(hereinafter, referred to as “ISC target torque” where appropriate) bythe ignition efficiency, which is a rate of torque decrease caused byretarding the ignition timing. A KL computation unit 1010 calculates atarget intake efficiency (hereinafter, referred to as “target KL” whereappropriate) based on the calculated target torque, the engine speed NE(current engine speed), and MBT (Minimum spark advance for Best Torque).The target KL is decreased (namely, the target torque that should beoutput from the engine 150 is decreased) until the target KL reaches theKL lower limit value of the target KL range (stored in a lower limitvalue storage unit 1020). When the target KL reaches the KL lower limitvalue, retardation of the ignition timing is started to decrease thetorque. A throttle valve opening amount calculation unit 1030 calculatesthe opening amount of the throttle valve 112 (hereinafter, referred toas “throttle valve opening amount” where appropriate) based on thetarget KL.

When the target KL reaches the KL lower limit value, the current intakeefficiency KL (hereinafter, referred to as “current KL” whereappropriate) is detected, and an ignition timing calculation unit 2000calculates the ignition timing based on the engine speed NE (currentengine speed), the current KL and the above-described target torque. Theignition timing is retarded (namely, the target torque that should beoutput from the engine 150 is decreased) until the ignition timingreaches the retardation limit timing of the ignition timing range(stored in a retardation limit timing storage unit 2010). When theignition timing reaches the retardation limit timing, a fuel-supplycutoff flag is set to decrease the fuel injection amount to zero.

In each of the case in which the target KL is decreased to the KL lowerlimit value and the case in which the ignition timing is retarded to theretardation limit timing, a fuel injection amount calculation unit(multiplier) 3000 calculates the amount of fuel injected from theinjector 126 by multiplying the current KL by the stoichiometric fuelinjection amount correction coefficient.

A selector 3010 selects the fuel injection amount calculated by themultiplier 3000 if the fuel-supply cutoff flag is not set, whereas itselects zero as the fuel injection amount (fuel injection cutoff) if thefuel-supply cutoff flag is set.

The control unit according to the embodiment of the invention may beimplemented by hardware formed mainly of a structure including a digitalcircuit or an analog circuit, or software formed mainly of a CPU(Central Processing Unit) and a memory included in the engine ECU 100and a program that is read from the memory and executed by the CPU. Ingeneral, implementing the control unit using hardware offers advantagesin the operation speed, and implementing the control unit using softwareoffers advantages in design change. The description below will beprovided on the assumption that the control unit is implemented bysoftware.

With reference to FIG. 3A and FIG. 3B, a description will be provided onthe control routine executed by the engine ECU 100, which is the controlunit according to the embodiment of the invention, when the fuel-supplycutoff is started. The control routine is a subroutine program that isperiodically executed at predetermined time intervals.

In step (hereinafter, referred to as “S”) 1000, the engine ECU 100detects various state quantities of the engine 150. The engine ECU 100detects, for example, the engine speed, the accelerator pedal operationamount, and the engine coolant temperature.

In S1010, the engine ECU 100 determines whether the fuel-supply cutoffcondition has been satisfied. At this time, the engine ECU 100 makes theabove-mentioned determination based on the engine speed, the acceleratorpedal operation amount, the engine coolant temperature, etc. detected inS1000. If it is determined that the fuel-supply cutoff condition hasbeen satisfied (“YES” in S1010), S1020 is executed. On the other hand,if it is determined that the fuel-supply cutoff condition has not beensatisfied (“NO” in S1010), S1000 is executed again. Because this routineis the subroutine program, if a negative determination is made in S1010,the process may return to the main routine.

In S1020, the engine ECU 100 calculates the target torque by multiplyingthe ISC target torque by the ignition efficiency. In S1030, the engineECU 100 detects the engine speed NE. In S1040, the engine ECU 100calculates the target KL using the function of which the variables arethe target torque, the engine speed NE and the MBT.

In S1050, the engine ECU 100 determines whether the target KL hasdecreased to the KL lower limit value. If it is determined that thetarget KL is equal to or lower than the KL lower limit value (“YES” inS1050), S1110 is executed. On the other hand, if it is determined thatthe target KL is higher than the KL lower limit value (“NO” in S1050),S1060 is executed.

In S1060, the engine ECU 100 calculates the opening amount of thethrottle valve 112 using the function of which the variable is thetarget KL. In S1070, the engine ECU 100 sets the ignition timing to thebase ignition timing.

In S1080, the engine ECU 100 detects the current intake efficiency(current KL). In S1090, the engine ECU 100 calculates the amount of fuelinjected from the injector 126 (fuel injection amount) by multiplyingthe target KL by the conversion coefficient.

In S1100, the engine ECU 100 transmits command signals that indicate thethrottle valve opening amount, the ignition timing and the fuelinjection amount which should be achieved when the intake efficiency KLis changing to a controller for controlling the opening amount of thethrottle valve 112, an ignition timing controller, and a fuel injectionamount controller, respectively. As a result, the target KL isdecreased, and the torque output from the engine 150 is decreased. Then,S1020 is executed again.

In S1110, the engine ECU 100 detects the current intake efficiency(current KL). In S1120, the engine ECU 100 calculates the targetignition timing (hereinafter, referred to as “target SA” whereappropriate) using the function of which the variables are the enginespeed NE, the current KL and the target torque.

In S1130, the engine ECU 100 determines whether the target SA hasreached the retardation limit timing. If it is determined that thetarget SA has reached the retardation limit timing (“YES” in S1130),S1180 is executed. On the other hand, if it is determined that thetarget SA has not reached the retardation limit (“NO” in S1130), S1140is executed.

In S1140, the engine ECU 100 sets the opening amount of the throttlevalve 112 to the opening amount that corresponds to the KL lower limit.In S1150, the engine ECU 100 sets the ignition timing to the target SA.In S1160, the engine ECU 100 calculates the amount of fuel injected fromthe injector 126 (fuel injection amount) by multiplying the target KL bythe conversion coefficient.

In S1170, the engine ECU 100 transmits command signals, which indicatethe throttle valve opening amount, the ignition timing and the fuelinjection amount that should be achieved when the ignition timing SA ischanging; to the controller for controlling the opening amount of thethrottle valve 112, the ignition timing controller, and the fuelinjection amount controller, respectively. As a result, the ignitiontiming is retarded, and the torque output from the engine 150 isdecreased. Then, S1120 is executed again.

In S1180, the engine ECU 100 sets the fuel-supply cutoff flag. Thus, thefuel supply to the engine 150 is actually cut off.

With reference to FIG. 4A and FIG. 4B, a description will be provided onthe control routine executed by the engine ECU 100, which is the controlunit according to the embodiment of the invention, when the fuel supplyis restarted. The control routine is a subroutine program that isperiodically executed at predetermined time intervals. In FIG. 4A andFIG. 4B, the steps that are the same as those in the flowchart in FIG.3A and FIG. 3B will be denoted by the same step numbers. Because theprocesses in the steps having the same step numbers are also the same,the detailed description thereof will not be provided below.

In S2000, the engine ECU 100 determines whether the torque required bythe driver has increased to a value equal to or higher than the lowerlimit torque (generable limit torque). If it is determined that thetorque required by the driver is equal to or higher than the lower limittorque (“YES” in S2000), S2010 is executed. On the other hand, if it isdetermined that the torque required by the driver is lower than thelower limit torque (“NO” in S2000), S2000 is executed again.

In S2010, the engine ECU 100 resets the fuel-supply cutoff flag. Thus,the fuel-supply cutoff is cancelled, and the fuel supply to the engine150 is actually restarted.

In S2020, the engine 100 detects the current intake efficiency (currentKL). Then, S1020, S1030 and S1120 are executed. In this process, theignition timing that has been retarded to the retardation limit timingis gradually advanced.

In S2030, the engine ECU 100 determines whether the target SA hasreached the base SA (base ignition timing). If it is determined that thetarget SA has reached the base SA (“YES” in S2030), S1040 is executed.On the other hand, if it is determined that the target SA has notreached the base SA (“NO” in S2030), S2040 is executed.

In S2040, the engine ECU 100 sets the opening amount of the throttlevalve 112 to the opening amount that corresponds to the current KL.Then, S1150, S1160 and S1170 are executed. In this process, the ignitiontiming is advanced and the torque output from the engine 150 isincreased. Then, S1020 is executed again.

When an affirmative determination is made in S2030, S1040, S1060, S1070,S1090 and S1100 are executed. In this process, the target KL isincreased and the torque output from the engine 150 is increased.

The fuel-supply cutoff operation of the engine 150 that is controlled bythe control unit (ECU) according to the embodiment of the invention,which has the above-described configuration and which executes theabove-described flowcharts, will be described with reference to FIG. 5(entire timing chart), FIG. 6 (detailed timing chart showing the statewhen the fuel-supply cutoff is started) and FIG. 7 (detailed timingchart showing the state when the fuel supply is restarted).

When Fuel-Supply Cutoff is Started

When the vehicle is traveling, if the driver does not depress theaccelerator pedal, for example, on a downhill slope, the fuel-supplycutoff condition is satisfied (“YES” in S1010). The fuel-supply cutoffcondition is satisfied at time t1 in FIG. 5.

The control unit according to the embodiment of the invention does notcut off the fuel supply at time t1. Instead, the control unit 1)decreases the KL to the KL lower limit to decrease the torque, 2)retards the ignition timing to the retardation limit timing to decreasethe torque when the KL reaches the KL lower limit, and 3) actually cutsoff the fuel supply when the ignition timing reaches the retardationlimit timing. The control unit actually cuts off the fuel supply at timet2.

More detailed description will be provided below with reference to FIG.6 (and FIG. 3A and FIG. 3B). FIG. 6 is a detailed timing chart thatcorresponds to the period from time t1 to time t2 in FIG. 5.

When the fuel-supply cutoff condition is satisfied at time t11 in FIG. 6(“YES” in S1010), the target torque is calculated by multiplying the ISCtarget torque by the ignition efficiency (S1020), the engine speed NE isdetected (S1030), and the target KL is calculated based on the targettorque, the engine speed NE and the MBT (S1040).

When the target KL has not reached the KL lower limit (“NO” in S1050),the opening amount of the throttle valve 112 is calculated based on thetarget KL (S1060), and the ignition timing is set to the base ignitiontiming (S1070). More specifically, first, the target KL is decreased todecrease the torque output from the engine 150 with the ignition timingkept unchanged. The fuel injection amount is calculated by multiplyingthe current KL by the conversion coefficient (S1090).

Command signals that indicate the calculated throttle valve openingamount, ignition timing and fuel injection amount are transmitted to thecontroller for controlling the opening amount of the throttle valve 112,the ignition timing controller and the fuel injection amount controller,respectively. This process is periodically executed until the target KLreaches the KL lower limit. As a result, the target KL is decreased andthe torque output from the engine 150 is decreased.

The duration of time until the target KL reaches the KL lower limitcorresponds to the period from time t11 to time t12 in FIG. 6. In thisperiod, the KL is decreased to the KL lower limit, and the torquegenerated by the engine 150 is smoothly decreased.

Next, when the target KL reaches the KL lower limit (“YES” in S1050),the current KL is detected (S1110), and the target SA is calculatedbased on the engine speed, the current KL and the target torque (S1120).When the target SA has not reached the retardation limit timing (“NO” inS1130), the opening amount of the throttle valve 112 is set to theopening amount that corresponds to the KL lower limit (S1140), and theignition timing is set to the target SA (S1150). More specifically,after the torque generated by the engine 150 is smoothly decreased bydecreasing the target KL (after the target KL reaches the KL lowerlimit), the ignition timing is retarded to decrease the torque outputfrom the engine 150. The fuel injection amount is calculated bymultiplying the current KL by the conversion coefficient (S1160).

Command signals that indicate the calculated throttle valve, ignitiontiming and fuel injection amount are transmitted to the controller forcontrolling the opening amount of the throttle valve 112, the ignitiontiming controller, and the fuel injection amount controller,respectively. This process is periodically executed until the target SAreaches the retardation limit timing. As a result, the target SA isretarded and the torque output from the engine 150 is decreased.

The duration of time until the target SA reaches the retardation limittiming corresponds to the period from time t12 to time t13 in FIG. 6. Inthis period, the ignition timing is retarded to the retardation limittiming, and the torque generated by the engine 150 is smoothlydecreased.

When the target SA reaches the retardation limit timing (“YES” inS1130), the fuel-supply cutoff flag is set and the fuel supply isactually cut off (S1180). The fuel supply is actually cut off at timet13 in FIG. 6.

When the fuel-supply cutoff is started, first, the target KL isdecreased to the KL lower limit to decrease the torque output from theengine 150. Then, the target SA is retarded to the retardation limittiming to decrease the torque output from the engine 150. Because thefuel supply is actually cut off after the torque output from the engine150 is smoothly decreased by a sufficient amount, the amount of astepwise change in the torque is reduced. Therefore, it is possible toreduce a shock that is caused when the fuel-supply cutoff is started.

When Fuel Supply is Restarted

While the fuel supply is cut off, for example, if the torque required bythe driver is equal to or higher than the generable limit torque (lowerlimit torque), the fuel supply is restarted (“YES” in S2000: S2010). Thefuel supply is restarted at time t3 in FIG. 5.

Immediately after the fuel supply is restarted, the control unitaccording to the embodiment of the invention 4) advances the ignitiontiming to the base ignition timing to increase the torque, and 5)increase the KL to increase the torque when the ignition timing reachesthe base ignition timing.

More detailed description will be provided below with reference to FIG.7 (and FIG. 4A and FIG. 4B). FIG. 7 is a detailed timing chart thatcorresponds to the period around time t3 in FIG. 5.

In the case where the torque required by the driver when the acceleratorpedal is released is set to be equal to or lower than the lower limittorque (generable torque), if the torque required by the driver is equalto or higher than the lower limit torque at time t21 in FIG. 7 (“YES” inS2000), the fuel-supply cutoff flag is reset and the fuel supply to theengine 150 is restarted (S2010). The current KL is detected (S2020), thetarget torque is calculated by multiplying the ISC target torque by theignition efficiency (S1020), the engine speed NE is detected (S1030),and the target SA is calculated based on the engine speed NE, thecurrent KL, and the target torque (S1120).

When the target. SA has not reached the base SA (“NO” in S2030), theopening amount of the throttle valve 112 is set to the opening amountthat corresponds to the current KL (S2040), and the ignition timing isset to the target SA (S1150). More specifically, first, the ignitiontiming is advanced with the target KL kept unchanged to increase thetorque output from the engine 150. The fuel injection amount iscalculated by multiplying the current KL by the conversion coefficient(S1160).

Command signals that indicate the calculated throttle valve openingamount, ignition timing and fuel injection amount are transmitted to thecontroller for controlling the opening amount of the throttle valve 112,the ignition timing controller and the fuel injection amount controller,respectively. This process is periodically executed until the target SAreaches the base ignition timing, and the ignition timing is advancedand the torque output from the engine 150 is increased.

The duration of time until the target SA reaches the base SA correspondsto the period from time t21 to time t22 in FIG. 7. In this period, theignition timing is advanced from the retardation limit timing to thebase SA, and the torque generated by the engine 150 is smoothlyincreased.

Next, when the target SA reaches the base SA (“YES” in S2030), thetarget KL is calculated based on the target torque, the engine speed andthe MBT (S1040). The opening amount of the throttle valve 112 is set tothe opening amount that corresponds to the target KL (S1060), and theignition timing is set to the base ignition timing (S1070). Morespecifically, after the ignition timing is advanced to the base ignitiontiming to smoothly increase the torque generated by the engine 150(after the target SA reaches the base SA), the target KL is increased toincrease the torque output from the engine 150. The fuel injectionamount is calculated by multiplying the current KL by the conversioncoefficient (S1090).

Command signals that indicate the calculated throttle valve openingamount, ignition timing and fuel injection amount are transmitted to thecontroller for controlling the opening amount of the throttle valve 112,the ignition timing controller and the fuel injection amount controller,respectively. This process is periodically executed based on the targetKL which corresponds to the torque required by the driver, and thetorque output from the engine 150 is increased.

The duration of time in which the target KL is increased and the torqueoutput from the engine 150 increases corresponds to the period aftertime t22 in FIG. 7. In this period, the ignition timing is maintained atthe base ignition timing, and the torque generated by the engine 150 issmoothly increased with an increase in the target KL.

When the fuel supply is restarted, first, the target SA is advanced tothe base ignition timing to increase the torque output from the engine150. Then, the target KL, which corresponds to the torque required bythe driver, is increased to increase the torque output from the engine150. Because the torque output from the engine 150 starts increasingimmediately after the fuel supply is restarted and increases smoothly bya sufficient amount, an amount of a stepwise change in the torque isreduced. Therefore, it is possible to reduce a shock that is caused whenthe torque required by the driver is increased and the fuel supply isrestarted. As a result, the driver feels sufficient acceleration feel,which improves the drivability.

The control described so far greatly differs from a non-torque-demandcontrol in which an engine is controlled (for example, the target KL ischanged) only based on the depression amount of an accelerator pedal.Under the non-torque-demand control, the target KL changes in accordancewith the depression amount of the accelerator pedal, which varies therate of increase in the torque. As a result, an acceleration shock (whenthe target KL increases abruptly because the accelerator pedal isdepressed suddenly by a large amount) or hesitation (when the target KLincreases slowly because the accelerator pedal is depressed gradually bya small amount) may be caused.

In contrast, the control unit according to the embodiment of theinvention executes the control described above. That is, A) immediatelybefore start of the fuel-supply cutoff, the control unit 1) decreasesthe KL to the KL lower limit to decrease the torque, 2) retards theignition timing to the retardation limit timing to decrease the torque,when the KL reaches the KL lower limit, and 3) actually cuts off thefuel supply when the ignition timing reaches the retardation limittiming. Then, B) immediately after the fuel supply is restarted, thecontrol unit 4) advances the ignition timing to the base ignition timingto increase the torque, and 5) increases the KL to increase the torquewhen the ignition timing reaches the base ignition timing. Therefore,with the control unit according to the embodiment of the invention, itis possible to minimize a shock that is likely to occur when thefuel-supply cutoff is started, and to minimize an acceleration shock andhesitation that are likely to occur when the fuel supply is restarted ina torque-demand engine control system.

FIRST MODIFIED EXAMPLE

Hereafter, a first modified example of the embodiment of the inventionwill be described with reference to FIG. 8. The first modified examplehas the following features in addition to the features of theabove-described embodiment.

When the accelerator pedal is released, the torque required by thedriver is decreased to the base torque. That is, the torque required bythe driver is not allowed to fall below the base torque. As shown inFIG. 8; the torque required by the driver matches the base torque.

The generable limit torque (lower limit torque) is set to the torquethat is generated at the ignition timing at which the intake efficiencyis decreased by the largest amount within a range, in which the fuelinjected from the injector 126 is ignited, at the engine speed NEcorresponding to the base torque.

When the condition that the torque required by the driver is lower thanthe generable limit torque is satisfied, the fuel supply is cut off.When the condition that the torque required by the driver is equal to orhigher than the generable limit torque is satisfied, fuel supply isrestarted.

According to the first modified example, it is possible to minimize ashock that is likely to occur when the fuel-supply cutoff control isstarted and to minimize an acceleration shock and hesitation that arelikely to occur when fuel supply is restarted, as in the embodiment ofthe invention described above.

SECOND MODIFIED EXAMPLE

Hereafter, a second modified example of the embodiment of the inventionwill be described with reference to FIG. 9. The second modified examplehas the following features in addition to the features of the embodimentof the invention described above.

In the second modified example, the base torque is set to the highestvalue from among a) the torque determined based on the target idlingtorque (ISC target torque), b) the torque determined based on the limitamount of fuel injected from the injector 126 (which is the minimumamount of fuel injected from the injector 126 and which is the lowerlimit of a range in which the linear relationship between the fuelinjection duration and the fuel injection amount is established), and c)the torque determined by multiplying the limit of a negative value in anintake pipe (due to consumption of, for example, engine oil) by the mostretarded angle (retardation limit).

According to the second modified example, the effects produced by theembodiment of the invention can be obtained. In addition, it is possibleto reliably obtain the torque that is determined based on the limitamount of fuel injected from the injector 126 and the torque that isdetermined by multiplying the limit of a negative value in the intakepipe (due to consumption of, for example, engine oil) by the mostretarded angle (retardation limit).

The embodiment of the invention that has been disclosed in thespecification is to be considered in all respects as illustrative andnot restrictive. The technical scope of the invention is defined byclaims, and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

1. A controller for a torque-demand-type internal combustion enginemounted in a vehicle, the controller comprising: a determination unitthat determines that a fuel-supply cutoff for cutting off a fuel supplyto the internal combustion engine is allowed to start when a state ofthe vehicle satisfies a predetermined fuel-supply cutoff startcondition; and a control unit that executes a torque-demand controlusing a relationship established among at least an intake efficiency, atorque and an engine rotational speed so as to decrease the torquegenerated by the internal combustion engine before executing thefuel-supply cutoff, when it is determined that the fuel-supply cutoff isallowed to start, wherein: the control unit includes an intakeefficiency control unit that decreases the intake efficiency of theinternal combustion engine to decrease the torque generated by theinternal combustion engine by changing the intake efficiency of theinternal combustion engine according to a target intake efficiencycalculated by a target torque of the internal combustion engine and acurrent engine rotational speed, and by changing a fuel injection amountaccording to the changed intake efficiency, until the target intakeefficiency reaches a predetermined lower limit value corresponding to alimit range in which the fuel injected from an injector is ignited, andan ignition timing control unit that retards ignition timing of theinternal combustion engine to decrease the torque generated by theinternal combustion engine, after the intake efficiency of the internalcombustion engine is decreased to the lower limit by the intakeefficiency control unit; and the control unit further includes afuel-supply cutoff control unit that controls the internal combustionengine to execute the fuel-supply cutoff after the ignition timing ofthe internal combustion engine is retarded.
 2. The controller accordingto claim 1, wherein the intake efficiency control unit decreases theintake efficiency to the predetermined lower limit value.
 3. Thecontroller according to claim 1, wherein the fuel-supply cutoff controlunit controls the internal combustion engine so that the fuel-supplycutoff is executed when the ignition timing of the internal combustionengine is retarded to a retardation limit timing.
 4. The controlleraccording to claim 3, wherein the predetermined fuel-supply cutoff startcondition is satisfied when a driver does not depress an acceleratorpedal while the vehicle is traveling on a downhill slope or when atorque required by the driver is lower than a torque that is generatedwhen the intake efficiency is decreased to the predetermined lower limitvalue.
 5. The controller according to claim 1, wherein the predeterminedfuel-supply cutoff start condition is satisfied when a driver does notdepress an accelerator pedal while the vehicle is traveling on adownhill slope or when a torque required by the driver is lower than atorque that is generated when the intake efficiency is decreased to thepredetermined lower limit value.
 6. The controller according to claim 1,wherein the ignition timing control unit retards the ignition timing toa predetermined retardation limit timing.
 7. The controller according toclaim 1, wherein the ignition timing control unit calculates theignition timing using an actual intake efficiency.
 8. The controlleraccording to claim 2, wherein the predetermined fuel-supply cutoff startcondition is satisfied when a driver does not depress an acceleratorpedal while the vehicle is traveling on a downhill slope or when atorque required by the driver is lower than a torque that is generatedwhen the intake efficiency is decreased to the predetermined lower limitvalue.
 9. The controller according to claim 2, wherein the fuel-supplycutoff control unit controls the internal combustion engine so that thefuel-supply cutoff is executed when the ignition timing of the internalcombustion engine is retarded to a retardation limit timing.
 10. Thecontroller according to claim 9, wherein the predetermined fuel-supplycutoff start condition is satisfied when a driver does not depress anaccelerator pedal while the vehicle is traveling on a downhill slope orwhen a torque required by the driver is lower than a torque that isgenerated when the intake efficiency is decreased to the predeterminedlower limit value.
 11. A controller for a torque-demand-type internalcombustion engine which is mounted in a vehicle and which is suitablefor a fuel-supply cutoff control, the controller comprising: a fuelsupply restart control unit that controls the internal combustion engineso that a fuel supply is restarted when a predetermined condition issatisfied while a fuel-supply cutoff for cutting off a fuel supply tothe internal combustion engine is executed; and a control unit thatexecutes a torque-demand control using a relationship established amongat least an intake efficiency, a torque and an engine speed, the controlunit being an electronic control unit, wherein: the control unitincludes an ignition timing control unit that advances ignition timingof the internal combustion engine to increase the torque generated bythe internal combustion engine when the fuel supply is restarted, and anintake efficiency control unit that increases the intake efficiency ofthe internal combustion engine to increase the torque generated by theinternal combustion engine after the ignition timing of the internalcombustion engine is advanced; the control unit controls the openingamount of a throttle valve, the ignition timing, and an amount of fuelinjected from an injector; the ignition timing control unit advances theignition timing to a predetermined reference ignition timing; and theignition timing control unit calculates the ignition timing using anactual intake efficiency.
 12. A method for controlling atorque-demand-type internal combustion engine mounted in a vehicle,comprising: determining that a fuel-supply cutoff for cutting off a fuelsupply to the internal combustion engine is allowed to start when astate of the vehicle satisfies a predetermined fuel-supply cutoff startcondition; and executing a torque-demand control using a relationshipestablished among at least an intake efficiency, a torque and an enginerotational speed so as to decrease the torque generated by the internalcombustion engine before executing the fuel-supply cutoff, when it isdetermined that the fuel-supply cutoff is allowed to start, wherein: inthe torque-demand control, the intake efficiency of the internalcombustion engine is decreased to decrease the torque generated by theinternal combustion engine by changing the intake efficiency of theinternal combustion engine according to a target intake efficiencycalculated by a target torque of the internal combustion engine and acurrent engine rotational speed, and by changing a fuel injection amountaccording to the changed intake efficiency, until the target intakeefficiency reaches a predetermined lower limit value corresponding to alimit range in which the fuel injected from an injector is ignited, andignition timing of the internal combustion engine is retarded todecrease the torque generated by the internal combustion engine afterthe intake efficiency of the internal combustion engine is decreased tothe lower limit; and the internal combustion engine is controlled toexecute the fuel-supply cutoff after the ignition timing of the internalcombustion engine is retarded.
 13. The method according to claim 12,wherein the ignition timing is retarded to a predetermined retardationlimit timing when the ignition timing is retarded.
 14. The methodaccording to claim 12, wherein the ignition timing is calculated usingan actual intake efficiency when the ignition timing is retarded. 15.The method according to claim 12, wherein the predetermined fuel-supplycutoff start condition is satisfied, when a driver does not depress anaccelerator pedal while the vehicle is traveling on a downhill slope orwhen a torque required by the driver is lower than a torque that isgenerated when the intake efficiency is decreased to the predeterminedlower limit value.
 16. The method according to claim 12, wherein theinternal combustion engine is controlled so that the fuel-supply cutoffis executed when the ignition timing of the internal combustion engineis retarded to a retardation limit timing.
 17. The method according toclaim 16, wherein the predetermined fuel-supply cutoff start conditionis satisfied, when a driver does not depress an accelerator pedal whilethe vehicle is traveling on a downhill slope or when a torque requiredby the driver is lower than a torque that is generated when the intakeefficiency is decreased to the predetermined lower limit value.
 18. Themethod according to claim 12, wherein the intake efficiency is decreasedto the predetermined lower limit value when the intake efficiency isdecreased.
 19. The method according to claim 18, wherein the internalcombustion engine is controlled so that the fuel-supply cutoff isexecuted when the ignition timing of the internal combustion engine isretarded to a retardation limit timing.
 20. The method according toclaim 19, wherein the predetermined fuel-supply cutoff start conditionis satisfied, when a driver does not depress an accelerator pedal whilethe vehicle is traveling on a downhill slope or when a torque requiredby the driver is lower than a torque that is generated when the intakeefficiency is decreased to the predetermined lower limit value.
 21. Themethod according to claim 18, wherein the predetermined fuel-supplycutoff start condition is satisfied, when a driver does not depress anaccelerator pedal while the vehicle is traveling on a downhill slope orwhen a torque required by the driver is lower than a torque that isgenerated when the intake efficiency is decreased to the predeterminedlower limit value.
 22. A method for controlling a torque-demand-typeinternal combustion engine which is mounted in a vehicle and which issuitable for a fuel-supply cutoff control, comprising: controlling theinternal combustion engine so that a fuel supply is restarted when apredetermined condition is satisfied while a fuel-supply cutoff forcutting off a fuel supply to the internal combustion engine is executedby an electronic control unit; and executing a torque-demand controlusing a relationship established among at least an intake efficiency, atorque and an engine speed, wherein: in the torque-demand control, whenthe fuel supply is restarted, ignition timing of the internal combustionengine is advanced to increase the torque generated by the internalcombustion engine; the electronic control unit controls the openingamount of a throttle valve, the ignition timing, and an amount of fuelinjected from an injector; the intake efficiency of the internalcombustion engine is increased to increase the torque generated by theinternal combustion engine after the ignition timing of the internalcombustion engine is advanced; the ignition timing is advanced topredetermined reference ignition timing when the ignition timing of theinternal combustion engine is advanced; and in the torque-demandcontrol, the ignition timing is calculated using an actual intakeefficiency.